SF Fire Department working to save a man who was buried in a mudslide. A woman was located and suffered non-life threatening injury.

SAN FRANCISCO (KTVU/AP) - A beach walk became a sudden tragedy Friday afternoon in San Francisco when a sandy cliff collapsed on two women, killing one of them.

It happened about 3 p.m. at Fort Funston, part of the Golden Gate National Recreational Area, in the southwest end of the city.

"We go all out on our rescue attempts," said San Francisco Fire Chief Joanne Hayes White, speaking to KTVU on the beach, as darkness fell. "These ones, these are tough, very tough."

As seen from SkyFox, a few dozen firefighters, trained in cliff rescue, dug determinedly with shovels for almost two hours.

"We believe the women were walking on the beach and then part of that cliff let loose and landed on them, and trapped them," said Hayes White.

There was hope the young woman might have survived in an air pocket, but that possibility faded as time passed. Search dogs could not pick up a trace, there was no cell phone ping, and metal detectors turned up nothing.

Grim-faced crews collected their equipment and trudged from the beach at about 5:30 p.m.

Chief Hayes White said it became dangerous for them to work beneath a cliff that was unstable and moving, especially after so much digging.

"We're in the business of saving lives, so this affects us," said Hayes White. "And someone lost a daughter, a sister, so this is tough."

The woman's companion, also in her early 20's, was rescued by a few other people on the beach.They pulled her out of the sand, which had buried her to the waist. She was in shock, but able to help arriving searchers identify where to begin looking for her lost companion.

Paramedics took her to the hospital to be checked, but her injuries were not serious.

"Who knows with all the rains we've had if that's made things worse," wondered one visitor, who saw the commotion on the beach.

"We see people all the time, climbing up the side of the hills, and you can tell they're unsafe," said his hiking companion.

Fort Funston is San Francisco's largest sand dune field, with cliffs 200 feet high.Remnants of old military bunkers cling to the bluffs, and some have already tumbled down. Signs warn visitors of the danger of unstable cliffs, and park regulars say they see the landscape shift, especially in winter.

"I don't get that close to the bluffs, I walk more towards the ocean," said one man, "and over the last month or two, they've collapsed quite a bit."

Said another park-goer: "I've been out here when little landslides have come down, and always kind of worried, if someone's too close, if that kind of thing can happen."

The fact that it did happen, is unusual, said the chief.

"We see a lot of surf rescues and cliff rescues in this city," said Hayes White, "But something like this in my 29 year career, I don't recall."

Fire crews, who tried so hard to save the woman's life, will be de-briefed about the incident and offered counseling.

"Even a year from now, someone who was here working hard digging to find this woman, could drive by or walk their dog, and this comes back to them, " said the Chief. "So we take that trauma seriously."